Since the past, a nitrile rubber (acrylonitrile-butadiene copolymer rubber) has been used as a material for rubber parts such as hoses, and tubes for automobiles by taking advantage of its oil resistance, mechanical properties, chemical resistance, etc. Further, a hydrogenated nitrile rubber (hydrogenated acrylonitrile-butadiene copolymer rubber) obtained by hydrogenating the carbon-carbon double bonds in the polymer main chain of the nitrile rubber is further excellent in heat resistance, so is being used for rubber parts such as belts, hoses, and diaphragms.
In view of such a situation, Patent Document 1 proposes a cross-linkable nitrile rubber composition containing a hydrogenated nitrile rubber having α,β-ethylenically unsaturated dicarboxylic acid monoester monomer units, a polyamine-based cross-linking agent, and a basic cross-linking accelerator. According to the cross-linkable nitrile rubber composition disclosed in Patent Document 1, the compression set resistance is improved, but the constant-elongation fatigue resistance is not sufficient. Therefore sometimes this is not suited to use for applications in which excellent constant-elongation fatigue resistance is required, for example, hose applications.